For detecting the limit level of liquids or bulk materials in containers, capacitive measuring equipment or vibration systems are installed. In addition to these limit level detectors, which signal the attainment of a predetermined fill level as soon as they come into contact with the process medium, there are contactlessly working measuring systems, which, as measuring radiation, use ultrasonic waves, microwaves—or in especially critical applications—radioactive radiation. With the exception of the vibration systems, the aforementioned measuring devices are naturally also suited for the continuous measurement of the fill level of a process medium in a container.
The measuring devices are normally sealed against the process. Depending on the application, it may be necessary to securely and reliably encapsulate the measuring device against the process and/or from a remote control station. This sealing or encapsulation is especially important when the atmosphere in the container is an aggressive or explosive one. If, for example, an explosive gas mixture penetrates into the housing of the measuring device, then, through direct contact with the electrical or electronic components of the measuring device, an acute danger of explosion exists. Furthermore, a measuring device is normally connected to a remote control station by means of connecting lines. If the measuring device is not encapsulated, then it cannot be ruled out that the explosive, aggressive, or toxic gas mixture will escape through the lines into the remote control station and do harm there.